1. Field of the Invention
The present invention relates to a light irradiation apparatus using an LED as a light source that is preferably used for spot illumination for product inspection, plant cultivation, or exhibits (pictures, foods, etc.).
2. Description of the Background Art
Recently, the high-intensity LED called the power LED, the blue LED, etc. have been developed, and along with these developments the LED are having greatly enlarged applications. For example, as a spot light irradiation apparatus for product inspection that is used for detecting flaws of a product and reading a mark thereof, conventional one using a halogen lamp as its light source has been used. However, in recent years, irradiation apparatuses each of which uses the LED that is superior in a life, luminous intensity stability, fast response, efficiency, etc. have been developed. Moreover, since the LED emits a less amount of heat and is also excellent in controllability, the LED has newly attracted attention also as the light source for plant cultivation.
On the other hand, in order to guide the light emitted from the LED to the forward, optical units as described in the following patent documents 1, 2 have been developed.
An optical unit of the patent document 1 (called an optical coupler) is for guiding light emitted from the LED to a light guide, such as a transparent rod, with as less waste as possible, being used mainly for dental medical treatment. This optical coupler is equipped with a bowl shape body that is transparent and solid, and a recess part is provided on a base end face of the body. Then the light emitted from the LED disposed in the recess undergoes total reflection on a curvilinear side of the body, or directly, and is emitted from an apical surface of the body. The apical surface of the body is made flat and is so configured that its apical surface is closely contacted with a light guiding face of the light guide and substantially whole of the light emitted from the LED is guided into the light guide.
An optical unit (called a lens body) of patent document 2 has a central prism part and an outer-ring prism part, being configured to receive all the light from the LED by the lens body and emit it to a predetermined direction.
If such an optical unit is made to be built in a spot light irradiation apparatus, an optical irradiation efficiency will be improved further. However, each of what were described focused only on efficiency of casting the light from the LED forward, it cannot make the size of the light irradiation area adjustable by making a distance between the LED and the optical unit variable.
Patent-document 1: Japanese Unexamined Patent Publication No. 2003-227974
Patent document 2: Japanese Unexamined Patent Publication No. 2002-43629